Download 5003 - Cumberland Trucks

FAST BRAKE
Trouble-ShooTing guide
INDEX
INTRODUCTION.....................................3
PRECAUTIONS........................................3
INSPECTION............................................4
Q&A
• “Why does my spring brake have square
air-inlet ports?”..........................................5
• “Why is the yoke welded to the service
push-rod?”..............................................7
• “What do I do for a replacement?”..................7
• “What happens if I replace a long stroke
chamber with a different stroke unit?”.........9
• “What’s the readjustment limit for 3-inch
long stroke chambers?”................................9
• “Is the service side diaphragm different for
a 3-inch long stroke brake?”.........................10
• “The service brake is not applying
adequate force.”......................................10
• “The parking brake is not holding. There
is insufficient parking force.”..................16
• “The parking brake will not stay released
(dragging brakes).”.................................17
• “Service brakes apply or the service exhaust
valve leaks when air is applied to the
parking brake.” ................................ 21
NOTE....................................................21
PUBLICATIONS..................................23
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MGM BRAKES
wants to help you keep
your trucks, trailers and
buses on the road.
At MGM Brakes we know how important it
is to keep your vehicles on the road and out
of the garage, so the whole idea behind this
Fast Brake Trouble-Shooting Guide is to
answer questions you might have and help
you find a solution to problems—fast.
But first, here are a few common-sense
precautions to take before you start.
PRECAUTIONS
1. Be sure to turn-off the engine before you
work under any vehicle.
2. Always chock the wheels. Depleting air
system pressure may allow the vehicle to
roll. Keep your hands away from actuator
push-rods and slack adjusters; they may
apply as the system pressure drops.
3. Never connect or disconnect a hose or
line that contains air pressure. It may
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whip as air escapes. Never remove a
component or pipe plug unless you’re
sure that all system air pressure has been
depleted.
4. Never exceed recommended air pressure,
and always wear safety glasses while
working with air brake systems. Never
look directly into air lines or fittings, and
never direct them at anyone.
5. Never try to dismantle a component until
you have read and understand the recommended procedures. Some units contain
powerful springs and injury is possible if
they are not properly dismantled. Use
only the correct tools, and observe all
precautions relative to the use of those
tools.
INSPECTION
Before you begin testing the air brake system,
it’s important to perform the following
checks:
1. Examine all tubing and/or hoses for signs
of kinks or dents.
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2. Check all tubing and/or hoses for signs
of wear, drying out or damage due to
excessive heat.
3. Check the suspension of all tubing and/
or hoses. They should be supported and
should not vibrate. Position them so they
will not be subject to excessive heat or
rub or wear against another part.
4. Determine the brand name, model and/
or part number of the spring brake.
Q &A
Now, you’re ready to start. Here’s a list of
commonly asked questions and complaints
(in red), along with possible causes and
recommendations on how to correct them.
“Why does my spring brake
have square air-inlet ports?”
Trucks, tractors, trailers and buses are being
manufactured with both standard 2.5-inch
stroke and 3-inch long stroke spring brakes
and service chambers, so it is important to
know how to identify what is on your
equipment.
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1. All 3-inch long stroke chambers can be
easily identified by their square air-inlet
ports (A), trapezoidal I.D. tags (B) and
servicing instructions embossed into the
aluminum center case (C).
2. Long stroke service chambers are
identified by a 1/2-inch high square, raised
embossment on top of the pressure cap
(D), along with the trapezoidal I.D. tag
(E) and embossed instructions on the
pressure cap (F).
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“Why is the yoke welded to
the service push-rod?”
Many 3-inch long stroke spring brakes and
service chambers are equipped with welded
yokes (G), which are permanently attached
to the service push-rod, making removal and
reuse virtually impossible.
“What do I do for a
replacement?”
Unless the non-pressure chamber (NPC, or
mounting base)(H), push-rod (I), and/or yoke
(J) have been damaged or are severely worn,
replacement of the single/piggyback unit
ONLY is recommended.
(NOTE: See MGM Brakes Product Bulletin 03-003)
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Otherwise, if replacement of the combination/
tandem unit is required, it should be replaced
with a welded yoke replacement unit ONLY.
(NOTE: See MGM Brakes Product Bulletin 03-003)
Do not attempt to replace a welded yoke
actuator with a universal “cut-to-fit”
aftermarket all-threaded push-rod
replacement unit. While it may be possible
to cut the push-rod at or near the correct
length, the combination of the threaded yoke
and jam nut (K) may prevent the unit from
achieving zero-stroke.
Also, if the push-rod opening in the nonpressure chamber (NPC, or mounting base)
is large enough, the jam nut will protrude into
the NPC and may damage the protective
stone shield.
(NOTE: See MGM Brakes Technical Bulletin 03-002)
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“What happens if I replace
a long stroke chamber with
a different stroke unit?”
Due to the difference in operational
characteristics of 2.5-inch and 3-inch stroke
chambers, mixing strokes across an axle may
cause an imbalance in the braking capability
of the vehicle. This may result in the vehicle
being “pulled” toward the side with the long
stroke unit during “emergency” stopping
situations.
IMPORTANT NOTE: When servicing a
truck/trailer/bus equipped with 3-inch long
stroke actuators, it is crucial that you replace
“like for like” and do not install a standard
2.5-inch stroke actuator in place of the long
stroke unit.
(NOTE: See MGM Brakes Technical Bulletin 02-002)
“What’s the readjustment
limit for 3-inch long stroke
chambers?”
The readjustment limit has been set at 2.50
inches for 3-inch long stroke actuators.
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“Is the service side
diaphragm different for a
3-inch long stroke brake?”
Yes. When replacing the service diaphragm
of a 3-inch long stroke chamber, you MUST
replace with a 3-inch long stroke diaphragm.
Installation of an incorrect diaphragm will
change the performance characteristics of the
actuator, adversely affecting its operating
efficiency, and may result in a catastrophic
failure.
“The service brake is not
applying adequate force.”
1. Improper brake adjustment.
With brakes applied, check the brake
chamber push-rod to see if the orange
MGM Brakes Stroke Alert stripe is
showing (L). If so, readjust the slack
adjuster in accordance with its
manufacturer’s instructions. Be certain
that the spring parking brake chamber is
fully released during this adjustment.
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2. Available air pressure to brake chamber
is insufficient (M).
Is the system air pressure gauge reading
normal? If it’s reading low, check
compressor for proper operation. Look
for kinked or blocked air lines. Check
for defective valves.
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3. Excessive brake lining or drum wear.
Handle in accordance with the
manufacturer’s inspection instructions.
Check brake chambers to ensure they are
fully released when brakes are not
applied. Also, check for incompatibility
of truck and trailer brake chambers.
4. Improper slack adjuster operation or
set-up.
The angle made by the brake actuator
push-rod with respect to the mounting
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surface should be perpendicular within
±3° from zero to full stroke. The pushrod clearance hole (N) in the non-pressure
chamber (NPC, or mounting base) for the
brake actuator push-rod should not be
elongated or show evidence of rubbing
or wear from the rod.
With brakes applied using 80-90 psi of
air pressure, the angle (O) between the
push-rod and slack adjuster should never
be less than 90°. Follow the slack adjuster
manufacturer’s recommendation for
proper operation and set-up.
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5. Damage to mounting bracket or
non-pressure chamber (NPC, or
mounting base).
Check bracket and NPC for cracks or
other signs of damage. Verify that
mounting nut torque is as specified in the
appropriate MGM Brakes Service
Manual.
If structural damage is found, replace the
defective parts immediately. Be sure to
follow MGM Brakes Service Manual
instructions for proper removal and
reinstallation.
6. Improper sizing of brake chambers or
excessive payload weight.
Consult with vehicle manufacturer, documentation or representative.
7. Brake chamber or air system (lines,
fittings, valves) leakage.
There may be a system leak if the
compressor comes on often, or pressure
is unable to be maintained.
Examine all lines, fittings and valves for
proper connection and leakage. If no
problems are found, inspect brake
chambers for leakage. Listen for an
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audible sound, or spray clampbands with
a soap/water solution and inspect for air
bubbles.
If leakage is found at the service side
clampband area, check the torque on
clampband bolts and verify it is adequate
per the appropriate MGM Brakes Service
Manual. If the leakage persists, replace
the diaphragm and clampbands per
instructions in the manual.
CAUTION:
If leakage is found at...
a. spring side crimp area
b. end plug
c. first valve in air line ahead of the
spring brake (emergency release)
...replace the valve (if required), or
replace the entire piggyback per
instructions in the appropriate MGM
Brakes Service Manual. Be sure to install
the release bolt and cage the spring by
following the manual’s instructions prior
to removal. Never attempt to open or
disassemble the single/piggyback
chamber on any spring brake.
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8. Improper push-rod length.
This may be the problem if proper rod
angularity is difficult to achieve, and/or
frequent readjustment is necessary.
Consult the vehicle manufacturer for
proper push-rod length.
“The parking brake is
not holding. There is
insufficient parking force.”
1. Refer to the possible causes just
discussed under “The service brake is
not applying adequate force.”
2. Broken power spring.
Remove the dust plug (P) from the release
bolt access hole of the brake chamber.
Use a flashlight to check for evidence of
spring breakage.
Brake chamber stroke (Q) can also be
checked while applying and releasing the
parking brake. If the expected range of
motion is not observed, the spring may
be broken. Also, the contents will rattle
if the piggy-back is removed and shaken,
indicating a probable broken spring.
Replace with the appropriate MGM
Brakes piggyback.
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“The parking brake
will not stay released
(dragging brakes).”
1. Available air pressure to the brake
chamber is insufficient.
Is the system air pressure gauge reading
normal? If it’s low, check the compressor
for proper operation. Look for kinked or
blocked air lines. Check for defective valves.
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2. Service application air is not exhausting
properly.
Apply and release service brakes while
listening to exhaust. If the sound is not
normal, check for kinked or blocked air
lines or defective valves.
3. The spring brake piston (R) is binding
before it is fully retracted.
Release the parking brake. Remove the
dust plug (P) and apply 90-100 psi of air
pressure. Look into the dust plug hole
to determine whether the gap (S) between
the top of the piston and spring chamber
housing (head) is approximately .200
inches. If not, replace the single
piggyback with an MGM Brakes
Piggyback or Piggyback ‘Plus’ Kit (kit
includes piggyback, clampband and
diaphragm).
4. Broken service chamber return spring (T).
Remove the piggyback and service
diaphragm (U), then inspect return spring
(T). If broken, replace with a new return
spring and new diaphragm. Order ONLY
genuine MGM Brakes brand replacement
parts and install in accordance with
instructions in the appropriate MGM
Brakes Service Manual.
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5. Ruptured diaphragm (V) or damaged
push-rod seal (W).
Check for leakage at the parking chamber
vent holes or through the release bolt
hole. Remove the release bolt access hole
dust cap (X) and apply air to spring brakes
(release). If you feel or hear air escaping
in these areas, the diaphragm is defective.
Replace entire piggyback as instructed in
appropriate MGM Brakes Service
Manual.
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If air applied to the spring chamber has
a tendency to apply the service brake or
to cause the service exhaust valve to leak,
the push-rod seal (W) is leaking. To
verify, disconnect the service air line and
apply air to the parking chamber. If air is
detected escaping through the open
service air-inlet port, the push-rod seal is
leaking. Replace the entire piggyback as
instructed in the appropriate MGM
Brakes Service Manual.
6. Autoslack over-adjustment or camshaft
linkage binding.
Consult the manufacturer’s service
manual.
7. Broken power spring (Y) or return
spring (Z) in parking brake section.
A broken power spring can be diagnosed
as discussed in the previous section.
A broken return spring in the parking
chamber is difficult to diagnose. Either
case requires the complete replacement
of the piggyback.
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“Service brakes apply or
the service exhaust valve
leaks when air is applied
to the parking brake.”
1. Air is leaking through the push-rod
seal (W).
Replace the entire piggyback as instructed
in the appropriate MGM Brakes Service
Manual.
NOTE
As the industry leader, MGM Brakes backs its
products with strong warranties—and an equally
strong commitment to the people and companies
who buy them. While the Fast Brake TroubleShooting Guide is a result of that dedication,
our commitment doesn’t end here.
The air-brake system is a complex web of valves,
tubing and other components and, try as we
might, it’s impossible to cover every troubleshooting eventuality. If you need advice on
problems that go beyond what we have presented
here, feel free to call your MGM Brakes Sales
Representative, or contact our Customer Service
Department at:
1-800-527-1534
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Please visit the MGM Brakes website at
www.MGMBrakes.com to reference our
publications including technical bulletins, service
manuals, product brochures and general catalog
information. All available literature can be
downloaded at your convenience—24 hours a
day, 7 days a week.
The MGM Brakes BrakeTECH Service SelfStudy Program is also available free of charge
and allows participants to learn common
procedures for maintaining and servicing spring
brakes and service chambers.
Also, keep in mind that most heavy-duty truck/
trailer/bus parts dealers and fleet specialists can
provide MGM Brakes product information and
genuine OEM service replacement assemblies.
At MGM Brakes, our commitment doesn’t stop
when you buy our products.
The way we see it, it’s just beginning.
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PUBLICATIONS
The following publications have been referenced in
this guide. All can be downloaded from the MGM
Brakes website where ‘hard copies’ can also be
requested.
Please visit our website or contact your local/regional
MGM Brakes representative for more information.
•
MGM Brakes Product Bulletin (03-003)
Replacement Units for MGM Brakes 3-Inch
Long Stroke Chambers with Welded Yokes
•
MGM Brakes Technical Bulletin (03-002)
Field Replacement of MGM Brakes Chambers
Equipped with Welded Yokes
•
MGM Brakes Technical Bulletin (02-002)
Mixing Standard & Long Stroke Chambers
•
MGM Brakes Model TR-Series Service
Manual (Form No. 5011)
•
MGM Brakes Model LTR-Series Service
Manual (Form No. 5042)
•
MGM Brakes Model MAGNUM
Performance Plus (MJ-Series) Service
Manual (Form No. 5044)
•
MGM Brakes BrakeTECH Service SelfStudy Training Program (Form No. 5043)
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